Add audio.

This is two questions.

The answer to the first is create a Coroutine that returns new WaitForSeconds(5) then calls Play on the audio source.

There are various answers to the second. Probably something elegant to do with colliders and/or triggers or something. You can also just put a script on the player that watches for when the player enters a certain zone by checking the player's position and then plays an audio source and disables or destroys itself.

Unless what you are looking for is to have a sound that seems like it is coming from a certain part of the game - like it gets louder when you get closer and quieter when you get further away. Something like a waterfall or whatever. That has to do with how you configure your audio source.